1. Field of the Invention
The present invention relates to a tone channel assignment apparatus for, e.g., an electronic keyboard instrument and, more particularly, to an apparatus suitably used in an electronic musical instrument for generating percussion tones such as drum tones according to key operations.
2. Description of the Related Art
In electronic keyboard instruments such as an electronic piano, an electronic organ, and the like, tone source data stored in a PCM waveform memory is read out according to a tone color and key data, and is output as a tone generation signal after its amplitude, envelope, and the like are processed. In order to generate tones corresponding to some simultaneously depressed keys or to generate accompaniment tones, a tone generator has a plurality of simultaneous tone channels.
A channel assignor manages tone channels, and assigns a tone to be generated in response to a key-ON event to an empty channel or a channel having a low priority order.
As a key assign method of the assignor, a first-depression priority method or a last-depression priority method is known. Also, the following method is known. In this method, when there is no empty channel, the envelopes of assigned tone waveforms are compared, and a new key is assigned to a tone channel having the lowest envelope level, i.e., a channel closer to the end of tone generation (envelope minimum value detection method).
An electronic keyboard which has the following play mode is known. In this play mode, instrument tones of a rhythm (percussion) section including drums, cymbals, and the like are assigned to some keys at, e.g., the left end side of a keyboard, so that a rhythm accompaniment play can be performed with the left hand simultaneously with a melody play with the right hand. In this mode, the keys of the rhythm section are also controlled under the channel assignment management of the above-mentioned assignor.
The assignor is generally constituted by a microprocessor and a program. The program executes real-time processing, and consists of a large number of steps. Thus, an expensive, high-speed microprocessor is required.
In an assignor which responds to only an ON/OFF event of a key, i.e., which operates independently of envelope levels, when there is no empty channel, unnatural channel assignment occurs inevitably. On the other hand, an assignor based on the envelope minimum value detection method requires a complicated arrangement and processing sequence although unnatural channel assignment can be eliminated.